A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a driver to a destination through a calculated route. Such a navigation system detects the position of the user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc, etc., or from a remote data server.
Typically, during a map mode, the navigation system displays a map image on a monitor screen while superimposing thereon a mark representing the current location of the user's vehicle. During a route guidance mode, the navigation system further displays a calculated route to the destination on the map image in a highlighted manner. At an intersection, if a turn is necessary, the navigation system notifies the user which direction to turn at the intersection such as by displaying an arrow image and generating audible instructions.
In displaying a map on a screen of a navigation system either on a map mode or a route guidance mode, information regarding a cross street ahead of the vehicle is useful for a user. Thus, a navigation system typically displays a name of the road on which the vehicle is currently running and a name of the next street that will intersect with the current street. However, some cross streets may not be very meaningful since the map data generally used in navigation system include road links that are not actually usable for vehicles of ordinary users or because of a particular location and direction of the vehicle, etc.
For instance, there is a cross street such as an emergency cross street on a freeway that is available to law enforcement vehicles but not generally available to the general public. In another instance, there is a cross road that merely connects two opposite sides of the road having a central divider. In a further instance, such a cross street or a road segment is meaningless if it not accessible for the user because it is a one-way street due to the particular location and direction of the vehicle.
Even when the next cross street is meaningless to a user as in the above example, the conventional navigation system shows the relevant information regarding the cross street. For example, FIG. 1A is a schematic diagram showing an example of display screen in which the navigation system displays the next cross street that is illustrated “UNKNOWN” because a particular cross street that comes next is not named and is not usable by a user. Such a display of known or unknown name of meaningless cross street is useless for a user and may be distracting to the safe driving.
Moreover, even when there is a meaningful next cross street, there may be a plurality of possible candidate names at an intersection when the name of each road that connected to the next cross street is different from one another. Such a situation is shown in the schematic diagram. of FIG. 1B which shows that the vehicle position 78 is moving on a street “Harvard Avenue” toward an intersection 76. In this example, the name of the street running in a left/right direction changes from “Edinger Avenue” (left side) to “Irvine Center Drive” (right side), or vice versa, at the intersection 76.
In the example of FIG. 1B, the navigation system will have to determine which name is likely to be more meaningful to the user. There may be even more complex situations where more than two streets of different names connect to an intersection. Thus, there is a need of new method and apparatus to determine whether a next cross street is meaningful enough to display, and if so, which name is the most meaningful and helpful to the driver. Further, there is a need of new method and apparatus to determine whether a cross street associated with a unique street type such as a double-digitized road is meaningful to the user.